Twin arc lamp



May 14, 1940- E. G. AsHcRAFT 2,200,483

TWIN ARC LAMP Filed lay 10, 1938 5 Sheets-Sheet 1 May 14, 1940- E.l G.A'sHcRAFT 2,200,483

TWIN ARC LAMP Filed May l0. 1938 5 Sheets-Sheet 2 May 14 1940- E..G.AsHcRAr-'T 2,200,483

TWIN ARC LAMP Filed lay l0, 1938 5 Sheets-Sheet C5 /nl/enor. Ernes 6.Hshdra i".

May 14 1940- E. G. AsHcRAr-T 2,200,483

TWIN ARC LAMP Filed lay 10. 1938 5 Sheets-Sheet 4 Mmmm May 14, 1940E..G. ASHCRAFT 2,200,483

. TWIN ARC LAMP Filed lay 10, 1938 5 Sheets-Sheet 5 Fly. 6..

'orney.

Patented May 14, 1940 UNITED STATES PATENT OFFlCE 9 Claims.

This invention relates generally to are lamps, and more particularly toarc lamps adapted especially for motion picture studio service,particularly for color photography, though not necessarily restricted tosuch service. A specic illustrative form of the invention relates to atype of studio arc lamp in which the carbone are disposed in verticalalignment, and is here illustratively described in a twin arc form, inwhich two p-airs of vertically aligned carbons are employed.

The vertical carbon twin-arc lamp as heretofore known in motion picturestudio practice, employing an intermittent gravity feed. principle foradvancing the upper carbons to compensate for consumption, is no longerconsidered appropriate for color picture service, since, owing to theintermittent feed, the intensity of the arc as well as its spectraldistribution is subject to variation of a character readily perceptiblein the nal picture.

In some types of twin arc lamps difficulty has been encountered due tothe tendency of one pair of carbonsto be consumed at a slightly fasterrate than the other. The diferential in the rate of consumption is notgreat for modern well made carbons, but if no equaliaing provisions aremade, the difference in gap length of the two arcs may becomeappreciable before the carbons are completely used.

It is accordingly a primary object of the invention to provide an arclamp capable of maintaining the spectral distribution of its emittedlight substantially constant under all conditions.

A further primary object of the invention is to provide improved carbonfeeding means capable of automatically maintaining a predetermineddistance of separation between the carbons of an arc lamp under alloperating conditions.

It is a further object of the invention to provide an improved twin ormultiple are carbon feeding mechanism in which the arc gaps areequalized from time to time.

A further important object of the invention is to provide an arc lamp ofthe character described with improved arc striking mechanism.

A further general object of the invention is to provide improved feedingand striking mechanism for an arc lamp of the type embodying verticalcarbons, capable of striking the arc by separating the carbons to apredetermined distance, and of maintaining said separation distanceconstant during operation of the lamp.

En accordance with the present invention, the carbone are fed toward oneanother' to compensate for consumption by an electric drive motor,preferably a shunt motor, which is connected across the arc, andprovisions are made whereby the voltage applied across the terminals ofthe motor for any line voltage within a substantial working range, e.g., 10E-l2() volts, is proper to cause the motor to drive at the speedrequired to feed the carbons at the rate necessary to just compensatefor consumption at that line voltage.

In accordance with a preferred embodiment of the invention, the arc lampmechanism is provided with upper and lower carbon carriages, which aregradually advanced toward one another by means of a lead screw driven bythe electric drive motor. rThe upper carbon carriage is adapted toloosely receive a carbon, or a pair or a multiplicity of carbons, forvertical movement therethrough, so that the upper carbons descend bygravity through the upper carriage and into engagement with the lowercarbons when the are is extinguished. The lower carbons are preferablyrigidly mounted on the lower carbon carriage. Means, preferably of asolenoid type, are mounted directly on the upper carbon carriage forgrip-ping the upper carbons and lifting them relatively to the uppercarbon carriageto strike the are when an electrical current is passedthrough the carbons. When the arc is extinguished, the two upper carbonsdescend by gravity into engagement with the lower carbons. When the areis again struck, the carbon lifting means on the upper carriage engagesthe two upper carbons and lifts them both exactly the same distance, tostrike the arc and to position them at the proper distance of separationfrom the lower carbone. The arc gap lengths are thus equalized each timethe are is extinguished and reignited. During burning of the arcs, thecarbons are advanced toward one another at a speed which issubstantially equal to their rate of consumption, as mentionedpreviously, so that the desired arc gap lengths are closely maintained.

The invention will be best understood by now referring to the followingdetailed description of illustrative means embodying the invention,reference being directed to the accompanying drawings, in which:

Fig. l is a front elevation of the mechanism; shown in inoperativeposition, with the carbons touching;

Fig. 2 is a top plan view of the mechanism of Fig. 1;

Fig. 3 is a side elevation, parts being broken z-iway, of the mechanismof Fig. l;

Fig. 3a is a detail section taken on line 3ft-3a of Fig. 3;

Fig. 4 is an enlarged view of a portion of Fig. 1, showing the mechanismin operating position;

Fig. 5 is a section taken as indicated by the broken line 5-5 of Fig. 3;

Fig. 6 is a section taken on line 6 6 of Fig. 3;

Fig. '1 shows the electrical circuit of the arc lamp; and

Figs. 8 and 9 are graphs illustrating relations provided in accordancewith the invention.

I will describe first one form of arc lamp mechanism illustrative ofsuitable means for carrying the present invention into practical effect.

Any suitable frame may be provided; as here illustratively shown, theframe includes upper and lower ycastings I and II connected by parallelvertical rods I2 and I3.

Tightly mounted on rods I2 and I3 are three mounting castings I4, I andI6, the rst being positioned at the upper ends of rods I2 and I3 justbelow upper frame member I0, the second being positioned midway of thelengths of rods I2 and I3, and the third being positioned at the lowerends of said rods, just above lower frame member II. Mounted onmountings |5 and I6 is the housing I1 for an electrical drive motor M,which is disposed with its drive shaft extending in a verticaldirection. This motor housing |1 is located just to the rear of theplane dened by rods I2 and I3, and just outside rod I2 (See Figs l and3).

Vertical motor drive-shaft I8 carries a worm I9, meshing with a wormwheel on shaft 2|, the latter having another worm 22 meshing with a wormwheel 23 tightly mounted on a vertically disposed lead screw 24. Belowworm wheel 23, lead screw 24 is provided with a downwardly extendingshaft portion 25 of reduced diameter, which is journaled, just belowworm 23, in a bearing 26 carried by mounting I5.

Bearing 26 has a shoulder at 21 resting on mounting l5, and its upperend supports lead screw 24 by engaging the undersurface of worm wheel23.

Pinned on shaft 25 below mounting I5 is a coaxial lead screw 30. Theupper end portion of lead screw 24 and the lower end portion of leadscrew 30 are suitably journaled in mountings I4 and I6, respectively.The upper carbon holder or carriage, designated generally by numeral 40,embodies a frame member a having hub portions 4I and 42 slidably mountedon parallel rods I2 and I3. Adjacent hub portion 42 frame 40a has a bore43 within which is received the upper end of a shaft 44 extendingdownwardly in parallelism with rods |2 and I3, shaft 44 being rigidlysecured to frame 40d as by pin 45. This shaft 44 is telescopicallyreceived by a tube 46 mounted at its lower end in mounting I6 andextending upwardly through a bore 41 in mounting I5, the upper end oftube terminating just above the latter.

A lower carbon holder or carriage 50 similarly comprises a frame 50aprovided with hub portions 5| and 52 slidably receiving rods I2 and I3,and having, adjacent hub portion 5|, a bore 53 receiving the lower endof a shaft 54 extending upwardly in parallelism with rods I2 and I3,shaft 54 being rigidly secured to carriage 50 as by means of pin 55.Carriage frame 50a is provided with a bore 56 which slidably passes theaforementioned iixed sleeve 46. Upwardly extending shaft 54 is slidablyreceived by a sleeve 51 rigidly mounted at its upper end on mountingmember I4 and extending downwardly therefrom through a bore 58 inmounting I5, the sleeve terminating just below mounting I5 as clearlyindicated in Fig. 4. Upper carbon carriage frame 40a is provided with abore 59 which slidably receives sleeve 51.

The upper and lower carbon carriages are thus mounted for verticalmovement along the described guide members. Releasable connections areprovided between said carriages and lead screws 24 and 30, which are ofopposite pitch, so that when said lead screws are rotated, the carboncarriages will be moved toward one another, and so that the connectionsbetween the carbon carriages and the lead screws may be released forquick adjustment oi the carriages along' the lead screws.

Thus the upper carbon carriage has a pair of vertically spacedrearwardly extending plates or brackets 65, between which are pivotallymounted a pair of levers 66. As shown in the drawings, each lever 06 hasa hub 61 pivotally mounted on a pin 68 extending between brackets 65.The forwardly extending arms 10 of levers 00 are provided with nutelements 1| adapted to threadly engage opposite sides of lead screw 24.A spring 14 between the rearward arms I5 of levers 56 spreads arms 15 tohold nut elements 1| in yielding engagement with lead screw 24. Therearward ends of arms 15 are provided with finger pieces 15 by whicharms 15 may be conveniently grasped to move them together for thepurpose of releasing 'threaded elements 1|, and therefore upper carboncarriage 40, from the lead screw.

Lower carbon carriage 50 is provided with rearwardly extending brackets80, between which are pivotally mounted manually releasable lead screwengaging levers 66 which may be exactly similar to the levers 00 on theupper carbon carriage, levers on the lower carriage having nut elements1| adapted to releasably engage lower lead screw member 30, as clearlyindicated in the drawings.

Lower carbon carriage 50 has two arms 90, to the outer ends of which aresecured carbon holders 9 I, which may be of any suitable type adapted toreceive and clamp the lower ends of a pair of vertical carbons 92. Ashere shown, holders 9| contain split bushings 9 I a adapted to clampcarbons 92 when screws 9|b are tightened. Carbon holders 9| are providedwith threaded studs 94 which extend through arms 90, nuts 95 beingscrewthreaded on said studs to secure the carbon holders in assemblywith the arms of the l carriage. Electrical connectors 96 clampedbetween nuts 95 serve to conduct electrical current to the carbonholders. The carbon holders and studs 94 are insulated from arms 90 bysuitable insulation such as indicated at 91.

Upper carbon carriage 40 has a forwardly extending bracket |00, to whichis secured a pair of diverging arms I0| and |02, each of which has, atits outer end, a pair of horizontal, vertically spaced brackets |03 and|04. The inner ends of arms |0| and 02 are perforated to receive screws|00 and surrounding insulation sleeves |01, screws |06 beingscrewthreaded into bracket |00, as clearly illustrated in Fig. 5.Insulation washers |08 insulate arms I0| and |02 from bracket |00.

Brackets |03 and |04 at the outer end of each of arms |0| and |02 areprovided, in alinement with lower carbons 92, with perforations |05 CIIadapted to slidably receive vertical upper carbons ll. Electricalconnectors lllJa are clamped directly on the upper ends of carbons llll.Carbons lill descend by gravity through brackets m3 and itil intoengagement with the upper ends of carhons all when the arc isextinguished, and are engaged and lifted with relation to the uppercarbon carriage to strike the arc by means supported by and travellingwith 'the carriage itself. While various means may be provided toaccomplish this purpose, I here i1 ustrate a simple mechanism comprisingcarbon engaging clutches in the form of flat plates l2il, one for eachcarbon, each having a carbon receiving perforation l2! midway betweenits ends which is somewhat larger in diameter than the diameter of thecarbon, and being positioned between the aforementioned brackets llltand lilrl, as illustrated. Clutch plates lli) normally, that is, whenthe arc is not burning, rest down on lower brackets lfl, illustrated inFig. l. Each plate lill has at one end a perforation l2?! somewhatloosely receiving a screw llltl which also downwardly through bracketllill. A nut llt on the lower end of screw 23. below bracket llll, is sopositioned as to permit plate l2@ to be lifted to the positionillustrated in Fig. 1l, at which point the head or the screw acts as astop preventing further upward move ment of the plate.

Plates lli are adapted to be lifted by means of links it@ connected totheir other ends, the latter being looped at their upper ends aroundinsulation sleeves mounted on a horizontal rod |3ll. Rod i3d passesthrough a central mounting |35, which is secured on and carried by theouter swinging end oi a lever member lli. Collars lllla set on rod onopposite sides of mounting |35 corinne the rod against endwisedisplacement.

As here illustratively shown, lever ltli is in the form of a rod whichis bent double, its two ends being received in openings lSl in mountinglilo, and being secured thereto by screws |313. The two arm portions ldtof the rod extending rearwardly from mounting. lao are bent upwardly atlts, so as to pass through loops Mil formed in the ends ot clips lillpivotally mounted at ldlc on arms lllti (see Fig. 5), and are then bentrearwardly, as at l 32, to form portions |123 passing around oppositesides of lead screw 24. The loop end oi the rod, rearwardly of leadscrew 2t, engages in a notch formed in the upper end of the verticallymovable plunger l5! of a solenoid .e pin 53 closes notch i553 above theloop end ot lever llit, so that when solenoid lll?! is energized andpulls plunger lill in a downward direction, pin. L53 will engage andpull down the loop end of lever |36. Lever lli is thus iucrumed bypivotally mounted clips lill. A liiii connected between mounting lllliand carriage frame dll returns lever 536 and solenoid plunger lill tothe positionoi Figs. l and 3 when the solenoid is deenergized.

Solenoid plunger lill is slide-ble through -a sleeve itil extendingthrough and tightly fitted in bracket arms between levers till (Fig. 5),the solenoid bei secured to the lower end of said sleeve, so that it ismounted directly on or is carried by the vertically travelling uppercarbon carriage. Thus, as illustratively shown in Fig. 3, the lowerportion of sleeve lftll is reduced, as at ll, and the case of solenoidis mounted thereon as by meansr of a press Fig. 'l shows the electricalcircuit for the arc lamp. The upper member of one pair of carbons isconnected by circuit conductor llll to one terrninal of the winding ofsolenoid lili, the other terminal of which is connected through a usualvoltage reducing resistance or grid lll and through line switch |96 tothe positive side of the line, as indicated. The lower carbon t2 of theother pair is connected by lead |12 through switch |90 to the negativeside of the line. The upper carbon of the latter pair and the lowercarbon of the Iformer are connected by a conductor Illia., so that the'two pairs of carbons are series connected across the line. The shuntdrive motor M for lead screws 24 and 3l) is connected by leads l 'irland |15 across the positive and negative leads ll'l and Il? going to thecarbone, one of said leads, here lead l'l5, including resistor lllic,which may be variable, and is so indicated in Fig. '2. The shunt fieldwinding f of motor M is preferably connected across resistor lla as wellas the armature of the motor, as indicated. With this arrangement, thespeed of the motor is more sensitive to the adjustment of resistor llct.I have stated that lead lll] goes to the positive side of the line andlead ll'2 to the negative side of the line; it is to be understood,however, that this is not necessary, and that the lamp will operate withthe reverse polarity as well. Resistor lll, ordinarily called the grid,is used since the usual available D. C. voltis excessive for the carbonsused in this type of lamp.

rilhe voltage across the motor armature during running conditions is thevoltage across the two series connected arcs, less the lR drop inresistor l'lc. Motor M runs at a speed proportional to Athis impressedvoltage, driving the two carbon carriages toward one another' tocompensate for consumption of the carbons.

When the arc is extinguished, the mechanism stands in the position ofFigs. l. and 3, with solenoid |52 deenergized, and lever llli held byspring |65 with its forward arm portions in downward position. Clutchplates l2@ are therefore resting on brackets ld, and upper carbone lillare free to slide by gravity through brackets H93 and itil until theirlower ends engage the upper ends of lower carbone When line switch |93is closed, electrical current flows through circuit llt, lill andthrough the carbone, then touching. Solenoid accordingly energized, andpulls plunger llil down. This swings lever lilli to elevate rod i3d,which lifts links ll to pull clutch plates to their upper, tiltedposition ol lig. ll. As the cli` ch plates are nrst tilted in thisaction, they d carbons lill, and as they are then elevated to theposition of Fig. Al, they lift the carbone, thereby striking the arc.The distance the carbone are lifted depends of course upon theadjustment ci stop screws 623, which are so adjusted that the carbonswill be lifted a distance exactly to the separation distance between thetips ol the carbons for proper operation. This separation distance istypically IIhe arc being struck, a potential difference is establishedthereacross, and shunt motor M begins to run. When the arc issubsequently extinguished, as by opening switch llill, solenoid ll isdeenergized, lever ltty is accordingly released and moves to allowclutch plates to descend to brackets Upper carbone llt are accordinglyreleased by the upper carriage, and descend by gravity until their lowerends engage the upper ends of lower carbons 92. When line fro switch isthen again closed, solenoid l5! is again energized and causes thecarbons to be lifted to strike the arc, the carbons again being moved atonce to their proper equal separation distance,

Thus it is characteristic of the invention that the upper carbons areloosely held by the upper carriage when the arc is extinguished, andthat when the arc is struck, means on the upper carriage engage theupper carbons and lift them by a distance equal to their normal distanceof separation from the lower carbons. The shunt drive motor driving theupper and lower carriages then closely maintains this separationdistance during burning of the arcs, as will be more fully discussedinfra.

It is an important feature of my invention that the separation distancesbetween the carbons are equalized each time the arc is extinguished andre-strucir, since the carbon holding clutch plates then take a new holdon the upper carbons and lift them both to exactly the same separationdistance from the lower carbons. In motion picture studio service thelamp of course does not normally burn for periods longer than say aboutten minutes at a time, and in such a short period of time no appreciabledifference in the distances of separation of the carbons, i. e., none ofwhich will have any noticeable effect on the quality of the light, willoccur. And since the separation distances of the carbons areautomatically equalized each time the arc is extinguished and re-struck,there is never any greater than a negligible differential between thelengths of the two gaps, and any such differential as may exist will beso slight that it may be disregarded.

When new carbons are to be placed in the lamp, levers 55 are operated torelease the carbon carriages from the lead screws, and the carriages maythen be readily and quickly moved to the outer ends of the guide rods.New carbons are then inserted, after which the lower carbon carriage isadjusted to bring the upper ends of the lower carbons to the properworking height. The lamp is then in readiness for operation.

Reference is now directed to Figs. 8 and. 9. Fig. 8 is a graph in whichcurve 2B!! represents the relation between the impressed line voltageand the average of the rates of consumption, in inches per hour, of thepositive and negative carbons of one arc. It is of course understoodthat, assuming equal diameter positive and negative carbons, thepositive carbon is consumed slightly faster than the negative carbon.Curve 23B does not express the exact rate of consumption of either thepositive or the negative carbon, but the average of the individual ratesof consumption of the two. The line voltage may be assumed to vary fromto 120 volts. This voltage is reduced somewhat by the drop acrossresistor lll, while the impressed voltage across each arc is of coursehalf of the voltage measured across the two pairs of carbons. Thus for aline voltage of volts, there may be an average potential of 33 voltsacross each arc. The curve of Fig. 8 thus represents the relationbetween the impressed line voltage and the average of the rates ofconsumption of the two carbons.

Fig. 9 shows two curves representing the relations for two differentlamp mechanisms between the impressed line voltage and the speed, ininches per hour, at which each one of the carbons is advanced. It willbe understood that the speed of advance of one of the carbons may becalculated by dividing the motor speed by the drive ratio between themotor and the speed of travel of the corresponding carriage or holderfor the carbon.

In the present embodiment of the invention, the speeds of the two carboncarriages are made equal, though it is obvious they may if desired bemade sufliciently `different so as just to compensate for the differencein rates of consumption of the positive and negative carbons. It will beevident that with the speeds of advance of the two carbons exactly equalto one another, and also maintained equal to the average of the rates ofconsumption of the positive and negative carbons, the position of thearc gap will gradually drift in the direction of the positive carbon, ata speed equal to the differential of the speed of consumption of thepositive and negative carbons. This drift is comparatively slight,however, and introduces no difliculty.

Curve 2li! represents a lamp mechanism in which, for one given linevoltage only, the rate of carbon feed is just equal to the average ofthe rates of carbon consumption for that given line voltage, as .readfrom the graph of Fig. 8. Thus, for voltage A, the rate of carbon feedis just equal to the average of the rates of carbon consumption, and ifthe graph of Figs. 8 and 9 were superimposed, curves 29B and 2li! wouldcoincide at one point a. At other impressed line voltages, however,there is no point of substantial coincidence on both curves ZUG and2531, and the carbons will therefor no longer be fed at rates equal totheir average rate of consumption, with the result that the arc gap willeither widen or close.

Curve 202 of Fig. 9 represents the condition established in accordancewith the present invention. By proper adjustment of the voltageimpressed across the drive motor, and proper choice of the drive ratiobetween the motor and the carbons, curve 202 is matched to curve 2% ofFig. 8, and if Figs. 8 and 9 were superimposed, curves 20!! and 282would approximately coincide for at least the range of impressed linevoltages for which the mechanism is designed, e. g., for a range of linevoltages ranging from 105-120 v. It will be evident from a comparison ofcurves 203 and 282 that for any line volage within the range from B toC, the rate of carbon feed will exactly or substantially equal theaverage of the rates of carbon consumption. Accordingly, assuming thecarbons to have initially been separated to a proper distance, thatdistance will be maintained regardless of variations in line voltage,the speed of the motor varying with changes in line voltage, but varyingalways so as to keep the rate of carbon feed equal to the average of therates of carbon consumption. The distance of carbon separation, andtherefore the spectral distribution of the emitted light, accordinglyremains constant for any change in line voltage at least as great asfrom 105 to 120 volts.

The method of and means by which the carbon feed characteristic forchanging impressed voltage is matched to the carbon consumptioncharacteristic for changing impressed voltage, as accomplished by thepresent invention, will now be described. The impressed linevoltage-carbon consumption characteristic curve is of course governed bythe consumption characteristics of the carbons to be used. The impressedline voltage-carbon feed characteristic depends upon several factors,among which are the magnitude of the voltage actually impressed acrossthe Sli terminals of the motor, and the drive ratio between the motorand the carbon advancing means. Accordingly, in the present simpleillustrative embodiment of the invention, resistor la is used in serieswith the armature of motor M, and preferably inside of field winding f,and this resistor is adjusted to establish the motor speedcharacteristic at such a value as will give the characteristic soughtfor a properly chosen drive ratio. It is believed the invention may bestbe illustrated by here giving data on one typical practical embodimentof the inveniton, though it is to be understood, of course, that thesefigures are illustrative only of one practical work-out of the inventionand are not to be taken in a limitative sense. With this understanding,it may be assumed that the lamp is to use cord, copper coated carbons,l-sg in diameter, of the type produced by National Carbon Co., and knownas Motion Picture Studo carbons. Resistance VH, usually known as thegrid, may be of a resistance of about 1.1 ohms, so that for a linevoltage of 115 v., the voltage across the series connected carbons willbe approximately 66 v., or 33 v. across each arc. Resistor I'iEa, isthen adjusted to a resistance of substantially 100 ohms. This resistancemay require somewhat ne adjustment to establish the precisecharacteristic sought. Motor M may typically be an ordinary 115 v.direct current shunt motor, rated at .5 a. and V40 H. P. The properdrive ratio between the shaft of motor M and each of the carbons is then1728 to 1.

A lamp mechanism having these characteristics maintains the lengths ofits two arc gaps very closely for variations in line voltage between 105and 120 V. Some slight change in gap length is detectable but notsufficient to vary the spectral distribution of the emitted light by adegree which is at all undesirable from the standpoint of motion picturecolor photography. Of course, under present studio conditions, a linevoltage variation of no greater than approximately four or ve Volts isordinarily encountered, and in present practice, therefore, it willordinarily be amply sufcient if the lamp maintains a substantiallyconstant gap for a range of line voltages as great as say four or vevolts. The degree of voltage variation necessary to be provided for willthus depend in given cases upon conditions as they are encountered instudio service. The specic lamp as herein disclosed is capable ofmaintaining a substantially constant gap for a wider range of linevoltages than is ordinarily met with, namely, for a range as great asfifteen volts. Such acondition is advantageous, however, even when theline voltage varies with a range of a very few volts, since with a lampdesigned to maintain the gapwidth substantially constant for a greaterrange of voltages than will actually ordinarily be encountered, there isassurance that the gap will be very steady with lesser voltagevariations than do occur with relative regularity.

The instantaneous voltage across one arc, if examined carefully, may befound to vary as much as plus or minus two volts in a somewhat irregularway due to air currents and non-uniformity of core materials of thecarbons. Voltage variations from this cause are transitory in character,however, and do not appreciably affect moto-r speed because of themomentum of the motor and parts driven thereby. Moreover, the plus andminus voltage variations when averaged over a short period of time willnearly cancel and for practical purposes may be neglected. Thevariations in voltage introduced by changing line voltage, on the otherhand, are essentially more gradual, and are the variations with whichthe present invention is concerned.

It is of course true that the intensity of the emitted Alight issubstantially lower at a line voltage of 105 v. than at a line voltageof 120 v. This condition is not at all serious, however, since it mayreadily be compensated by use of more or less lamps. What the presentlamp does accomplish, which so far as my knowledge goes, is entirelynovel, is to maintain the spectral distribution or color value of theemitted light substantially constant under all conditions encountered instudio service, an accomplishment of utmost importance to color motionpicture photography.

I have now illustrated my invention embodied in a twin arc type of lampemploying vertically alined carbons, in which both carbons are fed, andare fed at the same speed. It is of course obvious that my invention isalso applicable to other types of arc lamps, and is applicable whetherboth carbons of each arc are fed at the same or different speeds, oronly one carbon off each arc is fed. If but one carbon of each pair isfed, for example, it will simply be fed at twice the speed as in thecase of both carbons being fed at equal speeds. The fundamental basis ofthe invention, namely, matching of the impressed voltage-carbon feedcharacteristic to the impressed voltage-carbon consumptioncharacteristic, for the range of line voltage encountered in practice,rather than for a single line voltage, is thus applicable to all suchsituations. An arc lamp mechanism in accordance with the presentinvention is stable in operation` and maintains the predetermined lengthof its arc gap for all conditions encountered in the eld. No hand feedfor readjustment from time to time of the arc gap is required, and nooperator need stand in constant attendance. The lamp requires only thatthe arcs be struck, which is done automatically when the line switch isclosed, and then automatically maintains its arc gaps with all thenecessary constancy and accuracy called for by present color motionpicture photography practice without further attention.

I have now shown and described one present illustrative embodiment ofthe invention; it will of course be understood that this is forillustrative purposes only and that the present invention is applicableto other types of arc lamps as well. It should also be understood thatwhile I have referred to my invention chiefly in connection with colormotion picture photography, its full field of application is much widerthan this, as it is also applicable to projection of color motionpictures, or to studio or projector use with black and white lm, or toany other service calling for a stable arc lamp.

I claim:

l. In an arc lamp the combination of a frame, upper and lower carboncarriages mounted for vertical movement on said frame, drive means onsaid frame operatively connected with both said carbon carriages forcontinuously and uninter'ruptedly advancing said carriages toward oneanother, a carbon holder on said lower carbon carriage for tightlygripping a lower carbon, an upper carbon guide on said upper carboncarriage having a carbon guideway adapted for free passage of the uppercarbon and located in alinement with the lower carbon gripped by thecarbon holder on said lower carriage, and a carbon clutch and operatingmeans therefor associated with said upper carriage for gripping saidupper carbon and elevating it a predetermined distance through saidcarbon guide.

2. In an arc lamp, the combination of a frame, upper and lower carboncarriages mounted for vertical movement on said frame, drive means onsaid frame operatively connected with both said carbon carriages forcontinuously and uninterruptedly advancing said carriages toward oneanother, a carbon holder on said lower carbon carriage for tightlygripping a lower carbon, an upper carbon guide on said upper carboncarriage having a carbon guideway adapted for free passage of the uppercarbon and located in alinement with the lower carbon gripped by thecarbon holder on said lower carriage, and a carbon clutch and operatingmeans therefor mounted on and travelling with said upper cairiage forgripping said upper carbon and elevating it a predetermined distancethrough said carbon guide.

8. In an arc lamp the combination of a frame, upper and lower carboncarriages mounted for vertical movement on said frame, drive means onsaid frame operatively connected with both said carbon carriages forcontinuously and uninterruptedly advancing said carriages toward oneanother, a carbon holder on said lower carbon carriage for tightlygripping a lower carbon, an upper carbon guide on said upper carboncarriage having a carbon guideway adapted for free passage of the uppercarbon and located in alinement with the lower carbon gripped by thecarbon holder on the said lower carriage, a carbon clutch on said uppercarriage operable to grip and elevate said upper carbon a predetermineddistance through said carbon guide, and electromagnetic clutch operatingmeans mounted on said upper carriage and operatively connected with saidclutch in a manner to cause said clutch to grip and elevate said carbonwhen electrically energized and to hold said clutch in carbon elevatedposition until deenergized.

4. In an arc lamp, the combination of a frame, upper and lower carboncarriages mounted for vertical movement on said frame, drive means onSaid frame operatively connected with both said carbon carriages forcontinuously and uninterruptedly advancing said carriages toward oneanother', a carbon holder on said lower carbon carriage for tightlygripping a lower carbon, an upper carbon guide on said upper carboncarrage having a carbon guideway adapted for -free passage of the uppercarbon and located in alinement with the lower carbon gripped by thecarbon holder on the said lower carriage, a carbon clutch on said uppercarriage operable to grip and elevate said upper carbon a predetermineddistance through said carbon guide, electromagnetic clutch operatingmeans mounted on said upper carriage and operatively connected with saidclutch in a manner to cause said 'clutch to grip and elevate said carbonwhen electrically energized and to hold said clutch in carbon elevatedposition until deenergized, and an electrical energizing circuitconnecting said carbons and said electromagneticmeans in series.

5. In an arc lamp, the combination of upper and lower carbon supportingdevices, means on said lower carbon supporting device for gripping alower carbon, an upper carbon guide having a carbon guideway adapted forfree passage of the upper carbon and located in alinement with the lowercarbon gripped by the lower carbon supporting device, drive means foreffecting continuous uninterrupted relative movement of said carbonsupporting devices toward one another along a direction line parallel tosaid carbons, a normally released carbon gripping and lifting clutchassociated with the upper carbon-supporting device operable to grip andthen elevate the lowered upper carbon a predetermined distance relativeto the upper carbon-supporting device, a clutch-operating electromagnetmounted on the upper carbon supporting device and arranged for operationof said clutch to grip and so elevate said carbon when energized and tosustain said carbon in such relatively elevated position untildeenergized, and electrical connections through which said electromagnetis energized whenever electrical current passes through said carbons.

6. In an arc lamp, the combination of upper and lower carbon supportingdevices, means on said lower carbon supporting device for gripping alower carbon, an upper carbon guide on said upper carbon supportingdevice having a carbon guideway in alinement with said lower carbonsupporting device, drive means for effecting continuous uninterruptedrelative movement of said carbon supporting devices toward one another,an electromagnet mounted on said upper carbon supporting device, acarbon gripping and lifting member associated with the uppercarbon-supporting device comprising a clutch plate surrounding saidupper carbon and limitedly movable with relation to said carbonsupporting device between a lowered substantially horizontal positionand an upper tilted position, said plate releasably passing said carbonwhen in said lowered, substantially horizontal position, and grippingand then elevating said carbon when tilted and then elevated to saidupper, tilted position, means, including an operative connection withone end of said clutch plate, operated by said electromagnet to so tiltand elevate said clutch plate, and to sustain said clutch plate in saidtilted and elevated position until deenergized. and electricalconnections through which said electromagnet is energized.

'7. In an arc lamp, the combination of upper and lower carbon supportingdevices, means on said lower carbon supporting device for gripping andsupporting a plurality of lower carbons in parallel positions, acorresponding plurality of upper carbon guides on said upper carbonsupporting device having carbon guideways in alinement with therespective lower carbons, drive means for effecting continuousuninterrupted relative movement of said carbon supporting devices towardone another along a line of travel parallel to said carbons, and arcstriking means supported by the upper carbon-supporting device includinga plurality of carbon gripping and lifting devices normally releasedfrom the upper carbons, electromagnetic means operating said devices togrip and elevate said carbons a predetermined distance when energizedwith an electric current and to sustain said carbons in such relativelyelevated position until deenergized, and an electrical energizingcircuit connecting pairs of corresponding upper and lower carbons andsaid electromagnetic means in series.

8. In an arc lamp, the combination of a frame, upper and lower carboncarriages mounted for vertical movement on said frame, drive motor meanson said frame operatively connected with both said carbon carriages forcontinuously and imiiormly advancing said carriages toward one another,a carbon holder on said lower carbon CJI carriage for tightly gripping alower carbon, and an upper carbon clutch on said upper carriage forgripping the upper carbon when the latter is in end to end engagementwith the lower carbon and elevating it a predetermined distance relativeto the upper carbon carriage.

9. In an are lamp, the combination of a frame, upper and lower carboncarriages mounted for vertical movement on said frame, drive motor meanson said frame operatively connected with both said carbon carriages forcontinuously and uniformly advancing said carriages toward one another,a carbon holder on said lower carbon carriage for tightly gripping alower carbon, an upper carbon clutch on said upper carriage for grippingthe upper carbon when the latter is in end to end engagement with thelower carbon and elevating it a predetermined distance relative to theupper carbon carriage, and electromagnetic clutch operating means forcausing said clutch to grip and elevate said upper carbon, saidelectromagnetic means being mounted on and travelling with said uppervertically travelling 10 carriage.

ERNEST G, ASHCRAFT.

